The aim of this research is to quantitate non-polar halogenated hydrocarbon residues in skin lipids (sebum) of humans and to investigate the relationship of the kinds and concentrations of such compounds to those in other body tissues, i.e., blood and fat. While storage of these compounds in adipose tissue, with distribution to other tissues, is well known, and reflects exposure to chemicals in the environment, skin has not been studied. The skin is rich in lipids, and has been shown to be a major depot for such compounds in animals. The utility of sebum analysis would be advantageous, non-invasive, and relatively rapid to accomplish. Initial studies demonstrated that the (1) feasibility of collecting milligram amounts of lipid, using absorbent paper on the forehead, and (2) the detectability of p,p -DDE, the most common pesticide residue in humans, and PCBs (polychlorinated biphenyls) at levels similar to that found in adipose tissue. More recently, measurement of halogenated hydrocarbons including DDE, PCBs, HCB and chlordane residues has been reproducible at 0.05 ppm (hexachlorobenzene) to ca. 0.5 ppm (DDE, PCBs). Very high concentrations of certain PCBs have been observed in samples from workers exposed to PCBs. An effort is being made to ascertain whether this material has been merely deposited from ambient air or whether it represents a true skin secretion. Further studies are intended to standardize the sebum collection technique and to investigate the relative concentrations in blood, and where available, adipose tissue, of the major halogenated hydrocarbons present. Studies are under way for four populations with different chemical exposures.